Apparatus for separating solid particles from gaseous hydrocarbons have been available for years and have found commercial use, for instance in the separation of hydrocarbon cracking catalysts from gaseous products. As new, highly reactive cracking catalysts, such as zeolites, came into common usage, new separation apparatus were developed to rapidly separate the reactive cracking catalyst from the cracked hydrocarbon vapor in order to avoid overcracking once the hydrocarbons exit a reactor.
Van Den Akker et al, U.S. Pat. No. 4,961,863, and Ross, Jr. et al, U.S. Pat. No. 5,259,855 describe twin-drum separators which may be located at the terminal end of a catalytic cracking riser reactor. An advantage to twin drum separators is that they don't easily choke from catalyst carryover, but they have lower separation efficiency than some other available separators. Most catalytic cracking processes require a high separation efficiency in order to reduce the catalyst carried outside of the reactor vessels and, because of the lower separation efficiency of twin drum separators, these processes cannot use twin drum separators alone. The twin drum separators also do not integrate well with internal stripper beds because the upflow of vapor from the stripper catalyst bed disrupts the vertical flow within the twin drum separator.
Dewitz, U.S. Pat. No. 4,693,808, and Dewitz et al, U.S. Pat. No. 4,731,228 describe horizontal cyclone separators. The mass ratio of catalyst to gas in a horizontal separator limits the maximum amount of catalyst the separator can carry. If the mass ratio of catalyst to gas is too high, the horizontal cyclone separator tends to choke.
Parker et al, U.S. Pat. No. 4,692,311, describe a "quick disengaging cyclone" to reduce separating and stripping time. The cyclone works on centrifugal separation and a reverse flow vortex of vapor. A "vortex stabilizer means" is used to terminate the vortex before it reaches the bottom of the cyclone, where, if not terminated, the vortex can pick-up separated catalyst at the bottom of the cyclone and carry the catalyst back up and out through the cyclone outlet. The quick disengaging cyclone has proven to work at high efficiency; however, the unit is fairly large due to the need for an internal catalyst stripping bed and a standpipe extending from the bottom of the cyclone.
Fluidized catalytic crackers, fluid cokers, entrained coal gasifiers, and other industrial processes using fast-fluidized solids, may be retrofitted to achieve higher separation and stripping efficiencies in order to meet environmental and economic needs. While separator designs such as those just described have been used for retrofitting various fast-fluidized processes, their use can be limiting for retrofitting units which have limited space for placement of separators and strippers and/or which need to be retrofitted in order to increase efficiency.
In many catalytic cracking plants, for example, a riser reactor exhausts into a disengager vessel where undesirable post-riser cracking takes place. Most of these disengager vessels have a fluidized catalyst bed in the bottom and some sort of separation means at the top. These disengager vessels are often too small to be retrofitted internally with a separator/stripper such those just described. Moreover, it is expensive and inefficient to disassemble working catalytic crackers in order to install improved separators. So it has not always been possible, or desirable, to place higher-efficiency separators and strippers, such as those just described, into existing disengager vessels. It is very desirable to provide a separator/stripper technology which has high efficiency, smaller size, and simpler design.